On the trail of the beast

The Great Patriotic War. Soviet intelligence officers led by Sergei Skorin and Andrei Losev are trying to track down a well-organized sabotage group that is carrying out large-scale acts of sabotage in the rear of the Red Army in the lead-up to the Battle of Kursk. Andrei and Sergei are brothers, but they have been in a long-standing conflict. Andrei does not trust Sergei, as he suspects that his brother has been compromised.